JPH0734414Y2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a liquid crystal display device having a light-shielding film for negative display.

2. Description of the Related Art Conventionally, a liquid crystal display device that has been used for displaying instruments such as automobiles, clocks, etc., often employs a negative type display that displays bright characters and figures on a dark display surface.

In the negative type liquid crystal display device, since the voltage is not applied to the liquid crystal layer in the background portion other than the display portion, the liquid crystal molecules are twisted, and the light is twisted and advanced along this, and the polarization axes of the pair of polarizing films are changed. By arranging them in parallel, light is prevented from passing through in the background portion. However, in the background portion of a normal negative type liquid crystal display device, when the light twists and advances in the liquid crystal layer, the degree of polarization decreases, so that light of a specific color is transmitted to some extent, resulting in insufficient contrast. There was a problem.

In order to solve this problem, a light-shielding film is formed on the background portion other than the display portion by printing or the like.

[Problems to be Solved by the Invention] In order to prevent the display pattern from shifting from the pattern of the light-shielding film when viewed from an oblique direction,
It is usually formed inside the cell.

When this light-shielding film is a metal film, even if it is thin, the light-shielding degree is high, but since the conductivity is high, the insulation between the electrodes and the light-shielding film is perfect to prevent a short circuit between the electrodes. Had to do. However, with a thin insulating film, it is difficult to obtain an insulating film having a large area and no pinhole, and there has always been a risk of short circuit between adjacent electrodes.

Therefore, a thick light-shielding film is often formed by a printing method or the like. In the case of this thick film, there was almost no risk of short-circuiting between adjacent electrodes even if an ink using conductive particles such as carbon as a pigment was used. But,
Microscopic pinholes are likely to occur, causing light leakage.

In order to prevent this, it has been proposed to partially apply ink to the inner surface for repairing to prevent light leakage, or to attach a light-shielding film to the cell outer surface by printing or the like.

However, there is a problem of poor appearance due to color unevenness in the method of partially applying ink to the inner surface of the cell and correcting it,
In addition, printing on the outer surface of the cell requires printing for each single cell, which requires a lot of time and effort for production and also raises the cost.

As another method for preventing light leakage, there is a method of placing a light shielding plate on the front surface of the liquid crystal cell, but there is a drawback that the reflection color of the light shielding plate is noticeable, and it is very difficult to see, and therefore improvement has been desired.

[Means for Solving Problems] The present invention has been made to solve the above-mentioned problems, and a nematic liquid crystal layer is sandwiched between substrates provided with electrodes,
A negative-type liquid crystal display in which a pair of polarizing films are arranged on both surfaces of a liquid crystal cell provided with a light-shielding film except for a portion corresponding to a display pattern on the inner surfaces of the substrates facing each other, and a driving means for applying a voltage to electrodes is provided. In the display device, on the non-viewing side outside the liquid crystal cell, a liquid crystal display device, characterized in that a light-shielding plate provided with a light-shielding film other than a portion substantially corresponding to the display pattern is arranged substantially parallel to the substrate, and A part where the nematic liquid crystal layer is sandwiched between the substrates with electrodes, and where the polarization axis of the polarizing film is not applied to both sides of the liquid crystal cell where the light shielding film is provided except for the part corresponding to the display pattern on the inner surface of the opposing substrates. A pair of polarizing films are arranged so that light can be transmitted through, a driving means for applying a voltage to the electrodes is provided, and a voltage higher than that of the nematic liquid crystal is excited to the electrodes of the display pattern portion other than the desired display pattern. Negative to apply A liquid crystal display device for display, characterized in that a light-shielding plate provided with a light-shielding film on the surface other than the portion substantially corresponding to the display pattern is arranged on the non-viewing side outside the liquid crystal cell in substantially parallel to the substrate. A display device is provided.

Here, the non-viewing side of the liquid crystal cell means the side opposite to the viewing side of the liquid crystal cell by the observer.

In the liquid crystal display device of the present invention, since the light shielding plate is arranged on the non-viewing side of the cell, the thickness of the light shielding film can be made thinner than before, and the light leakage due to the pinhole as described above can be prevented. It is less likely to occur, and variations in shade of the printed film on the inner surface can be reduced, and further, the reflected color of the light shielding plate is not noticeable.

The present invention will be described with reference to the drawings.

FIG. 1 shows a sectional view of a basic example of a twisted nematic liquid crystal display device of a negative type display of the present invention.

In FIG. 1, 1A is a substrate, 2A is an electrode formed thereon, and an alignment film 3A is further formed thereon. On the other hand, the other substrate 1B has an electrode 2B thereon, a light-shielding film 4 on a portion other than the display pattern, and an alignment film thereon.
3B is formed. These two substrates are arranged so that the electrode surfaces thereof face each other, the periphery is sealed with a sealing material 5, and nematic liquid crystal is injected into the inside to form a liquid crystal layer 6 to form a liquid crystal cell.

Liquid crystal layer thickness (d) and refractive index anisotropy (Δn) of liquid crystal
It is desirable that the product Δn · d of Δ and d is in the range of 0.3 to 1.0 μm for the purpose of reducing the angle dependence of contrast and for increasing the transmittance of the translucent segment portion.

A light shielding plate 7 is provided on the non-viewing side of the liquid crystal cell. In the present invention, the light shielding plate 7 has a light shielding plate having an opening at a portion substantially corresponding to the display pattern.

Any material may be used for this light-shielding plate as long as it has a high light transmittance other than the light-shielding portion, and the material is not particularly limited. It may be a plate having a certain degree of rigidity or a flexible film.

A pair of polarizing films 8A and 8B are arranged on both surfaces of this liquid crystal cell.

As this substrate, a transparent substrate such as glass or plastic can be used, and a transparent electrode such as ITO (In ₂ O ₃ —SnO ₂ ) or SnO ₂ is formed on the surface thereof. Of course, this transparent electrode may be provided with a low-resistance metal lead, or a color filter, an insulating film, or the like may be formed above or below the transparent electrode.

The light-shielding film of the present invention has a light transmittance of 0.3% on the inner surface of the cell.
It is desirable to set it to 0.2% or less. In addition, the amount on the light shielding plate is preferably 1% or less, and more preferably 0.3% or less. By doing so, even if there is a portion such as a pinhole through which light partially exits, the pinhole can be made inconspicuous as a whole.

Note that the light-shielding film on the inner surface of the cell and the light-shielding film on the light-shielding plate are misaligned when viewed from an oblique direction, so the light-shielding plate is arranged on the non-viewing side of the liquid crystal cell, and the distance between the liquid crystal cell and the light-shielding plate is also increased. The light-shielding film on the light-shielding plate should have an opening 0.5 to 10 mm larger than the contour line of the opening of the light-shielding film provided on the inner surface of the liquid crystal cell, preferably 1 mm to 5 mm.

As the light-shielding film on the inner surface of the liquid crystal cell and the light-shielding plate, a conventionally known film for a light-shielding film can be used, and may be a thin film or a thick film. For example, it may be formed by printing or the like using an ink or the like containing a non-conductive pigment.

The light-shielding film on the inner surface of the liquid crystal cell is formed on the background portion of the display, and normally it may be formed on only one substrate. Of course, it may be formed separately on both substrates, but it is preferable to form it on one substrate because the number of steps is small and the productivity is good.

An alignment film is formed on the surface of the substrate with electrodes. When this light-shielding film is provided on the electrode, the alignment film is formed thereon. As this orientation control method, a known orientation control method such as a method of forming an organic polymer film of polyimide, polyamide, polyvinyl alcohol or the like by a printing method or a spinner method and rubbing it, or an oblique vapor deposition method can be used.

The alignment control direction of the alignment film may be usually 90 °,
In order to improve the contrast when viewed from an oblique direction, they may be shifted by about 50 to 120 ° and used.

Further, in order to improve the insulating property between this alignment film and the light-shielding film on the inner surface of the cell or the electrode, an insulating film such as SiO ₂ or TiO ₂ may be sandwiched.

The sealing material may be a normal sealing material such as epoxy resin or silicon resin. Usually, an opening is formed in a part of the sealing material, and after forming a cell, liquid crystal is injected from the opening and the opening is closed. It may be sealed.

As a liquid crystal to be injected, a small amount of a chiral substance is usually added to prevent it from having a spiral structure of reverse rotation, but when the twist angle determined by the orientation control direction is smaller than 90 °, no chiral substance is added. Liquid crystal can be used.

The polarization axes of the pair of polarizing films may be arranged substantially parallel to each other as in the case of a normal negative type liquid crystal display element, or may be substantially orthogonal to each other as in a normal positive type liquid crystal display element. May be arranged to do so.

However, when they are arranged so as to be orthogonal to each other, the portion to which a voltage is applied becomes black. Therefore, in contrast to the driving of a liquid crystal display element of a normal negative type display, the pixel to be brightened is not applied, and the pixel to be darkened is not. It is necessary to adopt the reverse driving method of applying voltage. Such a liquid crystal display device has an advantage that a high contrast ratio can be obtained as compared with a normal negative-type display liquid crystal display device because the dark portion has a higher light shielding degree.

When viewing from the front, the polarization axes are preferably parallel or orthogonal, but when viewing from an oblique direction and wanting to increase the contrast ratio when viewed from an oblique direction. In addition, it is preferable that the polarization axes are not orthogonal to each other but are displaced by 1 to 10 °.

As a driving means for applying a voltage to the electrodes, a driving means used in a normal liquid crystal display device can be used, and a driving means capable of supplying an AC voltage of a threshold value or more is usually used.

In addition, the substrate may be a polarizing film substrate, or a touch switch, an ultraviolet ray cut filter, or a non-reflection filter may be laminated on the outer surface of the substrate, as long as the effect of the present invention is not impaired. The technology applicable to the above may be applied.

The present invention can be used for a normal negative-type liquid crystal display device, but as described above, the pair of polarizing films are arranged so that the polarization axes thereof are orthogonal to each other, and the negative-type display is provided as a whole. The application of the voltage has a great effect when applied to a liquid crystal display device using a driving means which is similar to the positive type display.

That is, in the display portion of the pixel that transmits light, a voltage equal to or lower than the threshold value at which liquid crystal molecules rise is applied,
A voltage equal to or higher than the threshold voltage is applied to the light-shielded pixel. Regarding the method of applying the voltage, each pixel may be individually driven, or multiplex driving in which a plurality of pixels are driven by a common signal may be used.

As the driving voltage, a voltage that can obtain high contrast mainly at an observed angle may be selected. Generally, the higher the voltage is driven, the higher the angle (vertical direction to the substrate) and the higher the contrast can be obtained. When driven at a low voltage, high contrast can be obtained at a low angle, but when the voltage is too low, sufficient contrast cannot be obtained. In general,
It is desirable to drive within the range of 1.5 to 6 times the threshold voltage in the vertical direction.

Normally, an illuminating device is provided behind the polarizing film on the back surface for use, but a reflecting plate may be installed behind and a display may be performed using light from the front surface. Further, the present invention can be applied to an apparatus in which a lighting means and a semi-transmissive / semi-reflecting plate are installed and both the back and front lights are used. The illuminating means may be any one that emits light, such as a white light bulb or a cathode ray tube, and may be a means provided with a light control means for the amount of light.

Further, by adding a negative or positive dichroic dye to the liquid crystal, a higher contrast can be obtained with a wide viewing angle.

Further, an element having an appropriate optical anisotropy may be arranged between the pair of polarizing films to reduce the change in contrast angle.

The light shielding plate according to the present invention can take various forms within a range not impairing its function. For example, as described above, the film-shaped one may be attached to the illumination means. Further, particularly when this liquid crystal display device has a color filter outside the liquid crystal cell, a structure can be simplified by providing a light-shielding film on the color filter and also serving as the color filter. Therefore, it is very preferable in practical use.

[Operation] In the present invention, the light-shielding film on the light-shielding plate seems to have no apparent defect by blocking light leakage from the pinhole portion of the light-shielding film on the inner surface of the liquid crystal cell.

In this case, not only the light leakage but also the effect of eliminating the light and shade caused by the variation in the film thickness of the light-shielding film on the inner surface of the cell can be suppressed, and the individual variation of the liquid crystal display device can be suppressed and the stable quality can be maintained.

[Example] A glass substrate with ITO was patterned to form a light-shielding film with a thickness of 2.5 μm inside the cell by offset printing using a black ink except the portion corresponding to the display pattern, and the film was further formed thereon. Form a polyimide film with a thickness of 0.1 μm,
This was rubbed to form an alignment film to manufacture a segment electrode substrate.

Further, a glass substrate with ITO was patterned, a polyimide film having a film thickness of 0.1 μm was formed on the glass substrate, and this was rubbed to form an alignment film to manufacture a common electrode substrate.

The segment electrode substrate and the common electrode substrate are arranged so that the electrode surfaces face each other, and the periphery is sealed with a sealing material,
A liquid crystal cell was manufactured by injecting nematic liquid crystal into the inside.

A pair of polarizing plates was arranged on both sides of this liquid crystal cell, and a plate-shaped green color filter was arranged on the back side. Further, an illuminating means was arranged on the back side of this to prepare a liquid crystal display device.

At this time, one polarization film so that its polarization axis is orthogonal to the alignment treatment direction of the adjacent substrate, the other polarization film so that its polarization axis is parallel to the alignment treatment direction of the adjacent substrate,
That is, a pair of polarizing films were arranged so that their polarization axes were parallel to each other, and they were driven in the same manner as the driving of a normal negative-type liquid crystal display element. As a result, a negative type liquid crystal display device was obtained.

Next, the pair of polarizing films of the liquid crystal display device of this example are arranged so that their polarizing axes are orthogonal to the alignment treatment direction of the adjacent substrate, that is, the pair of polarizing films are arranged so that their polarizing axes are orthogonal. Contrary to the driving of a normal negative-type liquid crystal display element, a voltage was not applied to a pixel to be brightened, and a voltage was applied to a pixel to be darkened. As a result, in the portion corresponding to the display pattern, compared with the liquid crystal display device of the above-mentioned normal negative type, since the darkness is high in the portion corresponding to the display pattern,
The blackness of the background portion worked extremely effectively, and a liquid crystal display device having a high contrast ratio was obtained.

However, in the above-mentioned structure, if there is a pinhole in the light-shielding film on the inner surface of the liquid crystal cell, light will leak from the pinhole, and the light leakage cannot be completely prevented. Second
The figure is a front view of such a liquid crystal display element.
Eight pin holes 9 are formed in the light-shielding film 4 on the inner surface of the liquid crystal cell.
Something with a diameter of 2 mm has occurred. When the color filter 7'having a light-shielding film having a light-shielding film shown by the hatching in the broken line portion in FIG. 2 is arranged in place of the above-mentioned color filter, eight pinholes are formed on the color filter. It was hidden by the light-shielding film and disappeared, improving the appearance.

[Advantages of the Invention] In the liquid crystal display device of the present invention, since the light shielding film is provided on the inner surface of the cell and the light shielding film is provided on the light shielding plate outside the cell,
Due to the pinholes in the light-shielding film on the inner surface of the cell, it is not necessary to reproduce the light leakage defect and the workability is improved. Further, there is no shading due to variations in the light-shielding film on the inner surface of the cell, and the difference in appearance is reduced.

Moreover, since the light-shielding plate is provided on the non-viewing side of the cell,
There is little displacement of the light shielding film, and the reflection color of the light shielding plate is not noticeable.

Further, for the production of such a light-shielding plate, it is possible to print 100 sheets or more at a time by printing a patterned light-shielding film on one plate or film, and to cut it at a time, which is inexpensive. It can be manufactured without trouble.

In addition, the present invention can be applied in various ways within a range that does not impair the effects of the present invention.

[Brief description of drawings]

FIG. 1 is a sectional view of a basic example of a negative type liquid crystal display device of the present invention. FIG. 2 is a top view of the liquid crystal display device showing the arrangement of the light shielding film on the light shielding plate according to the present invention. Substrate: 1A, 1B Electrode: 2A, 2B Alignment film: 3A, 3B Light-shielding film: 4 Sealing material: 5 Liquid crystal layer: 6 Light-shielding plate with light-shielding film: 7 Polarizing film: 8A, 8B Pinhole: 9

Claims (4)

[Scope of utility model registration request] 1. A pair of polarizing films is provided on both sides of a liquid crystal cell in which a nematic liquid crystal layer is sandwiched between substrates provided with electrodes, and a light-shielding film is provided except for portions corresponding to display patterns on the inner surfaces of the substrates facing each other. In a negative type liquid crystal display device provided with a driving means for applying a voltage to an electrode, a light-shielding plate provided with a light-shielding film other than a portion substantially corresponding to the display pattern is provided on the non-visible side outside the liquid crystal cell. A liquid crystal display device, which is arranged substantially parallel to the substrate. 2. A polarization axis of a polarizing film on both surfaces of a liquid crystal cell in which a nematic liquid crystal layer is sandwiched between substrates provided with electrodes, and a light-shielding film is provided on portions of the inner surfaces of the opposing substrates which correspond to a display pattern. A pair of polarizing films are arranged so that light can be transmitted in the area where no voltage is applied, and driving means for applying voltage to the electrodes is provided, and the nematic liquid crystal is excited in the electrodes in the display pattern part other than the desired display pattern. In a negative-type liquid crystal display device that applies a voltage higher than the above, a light-shielding plate provided with a light-shielding film on the surface other than the portion substantially corresponding to the display pattern on the non-visible side outside the liquid crystal cell is substantially parallel to the substrate. A liquid crystal display device characterized by being arranged in. 3. The liquid crystal display device according to claim 1, wherein the light-shielding plate is a color filter having a light-shielding film provided on a surface thereof except for a portion substantially corresponding to the display pattern. 4. The light-shielding film provided on the light-shielding plate is a light-shielding film having a contour line opening which is 0.5 to 10 mm larger than the contour line of the opening portion of the light-shielding film provided inside the cell. The liquid crystal display device according to any one of claims 1 to 3.